President Barack Obama at once warned of an international cyber weapons arms race and subtly cautioned Russia and other adversaries that the United States has a greater capacity to wage cyber warfare than any other nation.

Speaking to reporters after the G-20 international summit in Hangzhou, China on Monday, Obama said he wanted to avert a new arms race between countries utilizing increasingly sophisticated cyber warfare techniques:

“We’ve had problems with cyber intrusions from Russia in the past, from other countries in the past. We’re moving into a new era here where a number of countries have significant capacities. And frankly, we’ve got more capacity than anybody, both offensively and defensively. But our goal is not to suddenly, in the cyber arena, duplicate a cycle of escalation that we saw when it comes to other arms races in the past, but rather to start instituting some norms so that everybody’s acting responsibly. We’re going to have enough problems in the cyber space with non-state actors who are engaging in theft and using the Internet for all kinds of illicit practices… What we cannot do is have a situation in which suddenly this becomes the wild, wild West, where countries that have significant cyber capacity start engaging in unhealthy competition or conflict through these means… That’s been a topic of conversation with [Russian] President Putin, as it has been with other countries.”

Russia is a leading suspect in an FBI investigation of a recent hacking attack on the Democratic National Committee in which some 20,000 internal emails, including proof that the DNC favored Hillary Clinton over Bernie Sanders in the Democratic primary, were leaked by the whistleblower website Wikileaks. In July, President Obama said he believed it was “possible” that Putin could be attempting to influence the outcome of the upcoming presidential election in favor of Republican nominee Donald Trump.

Russia has repeatedly denied the US hacking allegations, with Putin Internet advisor German Klimenko saying in June that “it’s easier to explain such things as intrigues of enemies than with one’s own incompetence.”

Critics say the rush to blame Russia for the DNC email hack is premature and that the DNC may have other motives in pointing the finger at the Kremlin.

Other countries and organizations including China, Iran, North Korea — which the US says was behind the 2015 attack on Sony Pictures Entertainment — and Islamic State have been named as bad actors in cyberspace by Lisa Monaco, Obama’s top homeland security and terrorism adviser.

The United States is also one of the world’s most prolific hackers. The US, along with Israel, are believed to have jointly developed the malicious computer worm Stuxnet during the 2000s to sabotage Iran’s nuclear program by destroying around 1,000 centrifuges that were enriching uranium. The US also attempted to launch a Stuxnet-type attack targeting North Korea’s nuclear program around the same time as the attack on Iran began, but operatives were unable to access critical computers and the operation failed. American cyber attacks also regularly target Islamic State and other terrorist networks.